One of the most important information to understand about your electric vehicle is the state of charge. The battery’s state of charge (SOC) refers to how much charge, or energy, is left in the battery.

SOC is measured in percent, and it’s the same measurement as a gas tank fuel gauge in a fuel-powered vehicle.

There are two types of SOC used to describe the battery on a vehicle. One is called Operational SOC, and the second is Technical SOC. So, what’s the difference between the types?

To understand this it is important to know that EV batteries lose capacity if they are operated close to zero SOC, or spend a lot of time at or near full capacity. So, in order to protect battery life, most vehicle OEMs limit the usable range of SOC.

This limitation prevents drivers and operators from accidentally driving the vehicle to 0% SOC, and automatically stops charging before 100% SOC.

Going back to the gas tank, these limits are similar to the warning light that comes on your dash when there’s less than ¼ tank of fuel and the warning signs about topping up your gas tank. Both extremes are also harmful to your gas tank and engine.

Even though this SOC limitation serves a really good purpose, it also creates a bit of confusion around the actual usable SOC of an electric vehicle.

The usable amount is called operational SOC and is typically the only SOC visible to operators. It shows up on the vehicle’s dashboard. 💡 The energy contained in the Operational SOC should always be used for route planning.

Technical SOC is how much the battery holds with no limits, from completely empty to completely full. The energy contained in the Technical SOC often shows up in marketing announcements or vehicle spec sheets, but it should not be used for route planning or driving range estimates.

The difference between Operational and Technical SOC varies by manufacturer, but typical differences are around 20%.

For example: 0% Operational SOC would be 10% Technical SOC, and 100% Operational SOC would be 90% Technical SOC. The energy contained in the Operational SOC would be 240 kWh, but 300kWh in the Technical SOC.

Some manufacturers provide the option to go below 0% Operational SOC in an emergency, like if the vehicle is stuck in the road and needs a little energy to pull over. In that case, the number of times you can use this override is usually listed in your battery warranty.

We hope you find this information useful for the operation of your electric fleet and remember, the important things to know about your vehicle’s SOC are:

Does your vehicle already have
protective upper and lower limits on SOC?